Abstract: The use of liposomes as detectable reagents in solid-phase immunoassays has been explored in a flow injection immunoanalysis (FIIA) system. Model calculations are presented for FIIA based on the competitive binding of univalent analyte and multivalent liposomes to immobilized antibodies. Parameters such as binding constants, concentrations of liposomes and antibody, and steric hindrance are considered for their relative effects on detectable liposome signal response to analyte concentrations. Qualitative comparisons of the model with the experimental data are made. A mathematical model is derived for competitive binding of theophylline (I) and liposomes to anti-I antibodies immobilized on a glass bead in flow injection systems. The model was applied in the optimization of a concentration.-dependent flow injection immunoassay. Preliminary experimental results agreed with predicted results.

Abstract: The use of liposomes in immunoassays to provide encapsulated markers as signal enhancers is presented. The liposomes are spherical bi-layer vesicles that can entrap a water-soluble marker during their formation. The markers can be visible dyes, fluorescent dyes, chemi/bioluminescent substrates, electroactive species or enzymes. The liposome surface contains an analyte tag which binds to a cell surface antibody, the marker is then measured directly (visible dyes) or the liposome is lysed before measurement can be performed. The liposomes can be used in an enzyme-linked flow injection liposome immunoanalysis (FILIA) and a system for the detection of alachlor is outlined. The system used an immunoaffinity column containing immobilized antibodies and had a detection limit of 5 ppb alachlor. The liposome markers can also be mixed with sample and applied to plastic-backed nitrocellulose containing an antibody competition zone and a liposome capture zone to produce test strips, the color of the liposome capture zone being measured. The use of test strips for multi-analyte assays is discussed.